Firing has everything to do with it. It takes a herculean effort to fire one direct government employee. Replacing the prime contractor and their hundreds of employees and subcontractors' employees on a work order is much easier.

I once heard some "war stories" from someone who had previously worked in a state government office, about the fistfights that broke out between government employees, and the difficulties in keeping malware off the boss-of-the-boss's computer as he routinely visited NSFW sites on state-owned hardware during the workday. That stuff simply doesn't happen in workplaces where people can easily be fired for gross misconduct.

There's good money to be made in actually doing the work that government employees don't do. And that's why no one close to the matter makes a great deal of fuss about them not doing it. If the work needs to be done, and there is no way to force those nominally responsible for it to actually get it done, they can throw more budget at the problem and get a contractor. If you know enough about the problem to say why the direct employees can't fix it, you also know enough to do it yourself and get paid.